My invention relates to the art of batteries and more particularly to batteries discharged on immersion in salt or fresh water, or other electrolytic medium. While my invention is highly advantageous when embodied in a primary battery having a low discharge rate on immersion in an electrolyte, it is not limited to primary batteries, and secondary batteries made in accordance with the disclosure herein shall be deemed to come within the purview and scope of the invention and to be covered by this application. Batteries used for powering navigational aids, fiber optic communication systems, underwater sensors, underwater beacons, on-the-bottom surveillance buoys and passive underwater target detecting devices should meet the following requirements: (1) have high voltage: (2) be capable of being operated for long periods of time, preferably up to two years, without maintenance or replacement; and, (3) have relatively low cost. Previously known batteries have offered only a compromise between these three factors and have been additionally limited by the requirement that they must fit into the limited stowage space provided within the device itself.
Lithium thionyl chloride batteries in rigid, sealed containers now offer the lowest cost system available for powering deep sea devices, but this cost is extremely high for it is about $10,000 per watt-year of available energy.
Many types and varieties of water activated batteries have been developed and are available. Conventionally the magnesium/silver chloride couple is used in such designs principally for its volumetric compactness, ease of manufacture, and high discharge rate. Various electrochemically active alloys of magnesium, aluminum and/or zinc may alternatively be used as the anode material. Manganese dioxide, lead chloride, silver/cuprous chloride mixtures, cuprous thiocyanate as well as numerous organic halogenating agents may be used to depolarize the cathode. Alternatively a catalytic surface may be provided to evolve hydrogen at the cathode.
All of these types and varieties of water activated batteries are intended and designed to fit into a limited storage space in the form of an essentially rigid battery housing. This housing typically protects the battery cells from mechanical damage and in most cases provides rigid mechanical support for the battery electrodes, separators and electrolyte passages.
There are certain difficulties involved with the heretofore known and applied use of an essentially rigid battery housing for water activated batteries intended for operation for long periods of time. The electrochemical reactions during battery operation produce the deleterious buildup of reaction products on the electrode surfaces. The walls of the rigid housing enclosing the battery combines with the typically compact volumetric design to prevent the escape of these deleterious reaction products to the surrounding waters.
Several means and expedients have been used to attempt to avoid the deleterious buildup of heavy sludge, heat and/or reaction gases on the battery plates. Typically they involve attempting to assure a free and even circulation of electrolyte over the battery plates through pumping and/or through providing passages through the rigid housing for the natural circulation of water through the battery. These, however, are oftentimes expensive and/or tedious and difficult to effectuate rendering them impractical for low rate batteries despite their apparent value.
The basic characteristics and operational principles and limitations of water activated battery design and utilization practice are so widely comprehended by those skilled in the art that further elucidation thereof and elaboration thereon is unnecessary for thorough understanding and recognition of the advance contributed and made possible to achieve by and with the developments of the present invention.
An important object of my invention is to permit primary batteries having a low discharge rate on immersion in an electrolyte to operate for years at a time without suffering deleterious buildup of reaction products.
A further object is to give those skilled in the art of marine equipment design relief from the requirement that water activated batteries must fit into limited, and typically box like, stowage spaces.
Other objects of the present invention will be evident to those skilled in the art from the following detailed description and claims when read in conjunction with the accompanying drawings.